1. Field
This disclosure relates generally to semiconductor device structures, and more specifically, to protection of the gate dielectric in transistors.
2. Related Art
Boron penetration into gate dielectrics has been a long standing problem. The boron can come from either the gate side or the channel side. The gate side has generally been the greater problem because of the relatively higher boron concentration. This has been obviated in large measure through techniques using nitrogen or other blocking species such as carbon in the gate or at the top surface of the gate dielectric. Thinner gate dielectrics are desirable for improved transistor performance but are now resulting in an increased susceptibility to boron penetration from the channel side, especially from the source/drains of P channel transistors. Boron penetration has the effect of significantly increasing leakage and subsequently reducing the life of the device. Both gate dielectric leakage and device lifetime issues are important to be resolved in transistor development.
Thus, there is a need for reducing the presence of boron on the channel side of a gate dielectric while avoiding a significant reduction in device performance or at least while maintaining acceptable device performance.